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GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L04808, doi:10.1029/2007GL032523, 2008

Chemical composition of atmospheric nanoparticles formed from nucleation in Tecamac, Mexico: Evidence for an important role for organic species in nanoparticle growth

J. N. Smith

National Center for Atmospheric Research, Boulder, Colorado, USA


M. J. Dunn

National Center for Atmospheric Research, Boulder, Colorado, USA


T. M. VanReken

National Center for Atmospheric Research, Boulder, Colorado, USA
Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington, USA


K. Iida

Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, USA


M. R. Stolzenburg

Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, USA


P. H. McMurry

Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, USA


L. G. Huey

School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA


Abstract

We report Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS) measurements of the composition of ambient 10–33 nm diameter particles formed from nucleation on 16 March 2006 in Tecamac, Mexico during the Megacity Initiative: Local and Global Research Observations (MILAGRO) field study. On this day, nucleated particles contained far more organics than sulfates: average ion molar ratios with measurement uncertainties for nitrate, organics and sulfur species were 6 ± 2%, 84 ± 5%, and 10 ± 1%, respectively. The measured organic species include nitrogen-containing organic compounds, organic acids, and hydroxy organic acids. Independent calculations show that sulfuric acid condensation could have accounted for only 10 ± 2% of the growth that was observed on this day, which is consistent with the TDCIMS measurements of composition. It follows that organic compounds play a dominant role the high growth rates that were observed.

Received 30 October 2007; accepted 18 January 2008; published 22 February 2008.

Keywords: nucleation; aerosol; MILAGRO.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0394 Atmospheric Composition and Structure: Instruments and techniques.

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Citation: Smith, J. N., M. J. Dunn, T. M. VanReken, K. Iida, M. R. Stolzenburg, P. H. McMurry, and L. G. Huey (2008), Chemical composition of atmospheric nanoparticles formed from nucleation in Tecamac, Mexico: Evidence for an important role for organic species in nanoparticle growth, Geophys. Res. Lett., 35, L04808, doi:10.1029/2007GL032523.